One form of apparatus to which the improvements according to the present invention are applicable is disclosed in U.S. Pat. Nos. 4,587,796 to HALOILA and U.S. Pat. No. 5,390,476 to MORANTZ, the disclosures of which are hereby incorporated by reference herein for background purposes. The apparatus disclosed in these patents includes a stationary frame for receiving an article or load to be wrapped, a vertically reciprocable frame supported on the stationary frame, and a ring member supported on the reciprocating frame for displacement therewith and for rotation relative thereto about a vertical ring axis. The ring member carries a film carriage assembly by which film is wrapped around a load during rotation of the ring member.
Heretofore, the ring member in such wrapping apparatus has been of metal construction fabricated from two matching pieces suitably secured together and machined in an effort to obtain the necessary accuracy and profile for rotating the ring at an acceptable speed with respect to achieving a desired wrapping rate. For all the effort in this respect, however, the ring is often out-of-round and/or not flat with respect to a plane transverse to the ring axis, and these problems limit the speed at which the ring can be rotated and thus the wrapping rate of the apparatus. Moreover, the ring generally has web and flange portions by which the ring is supported for rotation and, as a result of the out-of-round and non-flat problems, tracking of the ring relative to the rollers and wheels which support the ring for rotation is not good, and this too reduces the speed at which the ring can be rotated. Still further, the ring supports commutator or slip ring members by which electrical power is delivered to the carriage assembly during operation of the apparatus, and the foregoing problems with respect to the contour of the metal ring member cause relative bouncing between the moving, slip rings, and the fixed brush contacts therefor. Such bouncing causes arcing between the commutator rings and brushes, again limiting the speed at which the ring member can be rotated. Moreover, such bouncing increases the wear between and decreases the life of the slip rings and brush contacts, thus increasing the maintenance cost and time with respect to the apparatus.
The weight of the metal ring members, which are generally made from steel or aluminum, adds to the foregoing problems with respect to the contour and the effect of the contour on the ring speed. Especially in this respect, the weight of the metal rings affects the acceleration and deceleration rates of the ring with respect to a wrapping operation and, thus, the wrapping rate at which the apparatus can be operated. Still further, all of the foregoing problems are attendant to the use of metal rings with another form of wrapping apparatus in which the vertically reciprocable frame carrying the ring member is mounted in a cantilever fashion relative to the stationary frame. With this apparatus configuration, additional problems result from the weight of the ring. In this respect, the cantilever arrangement imposes undesirable bending forces between the stationary and reciprocating frames, thus requiring more rigid interengaging support arrangements and/or a counterweight arrangement and/or a positioning of the reciprocating frame relative to the stationary frame so as to shorten the length of the cantilever arm relative to the stationary frame. The latter arrangement, however, reduces the diameter of the ring member which can be used with the apparatus and, thus, the peripheral size of a load which can be wrapped by the apparatus.